Sodium soap grease containing a zinc salt of a dialkyl dithiophosphate



United States Patent 3,203,897 SODIUM SOAP GREASE CONTAINING A ZINC SALT 6F A DHALKYL DII'HHOPHOSPHATE Henry A. Ambrose, Penn Township, Allegheny County, and Paul R. McCarthy, Allison Park, Pa, assignors to Gulf Research 8; Development Company, Pittsburgh, Pa, a corporation of Delaware No Drawing. Filed Sept. 20, 1962, Ser. No. 225,130 3 Claims. (Cl. 252-323) This invention relates to improved grease compositions and more particularly to grease compositions having increased performance life at elevated temperatures.

Elevated temperatures such as those above 200 F. are frequently encountered in roller and ball bearings. When a conventional grease composition is used to lubricate such bearings, the grease may melt and run out of the bearing in which case effective lubrication takes place for a relatively short period of time. Conventional greases melting at high temperature will remain in such bearings but because of the high temperature will ordinarily oxidize or polymerize forming hard gummy deposits which increase torque and finally result in breakdown of the hearing. This problem is especially acute in connection with prepacked, sealed bearings which require effective lubrication over prolonged periods of time, much of which is at elevated temperatures.

It is an object achieved by this invention to provide an improved high temperature grease. A further object achieved by this invention is to provide a grease which will effectively lubricate roller and ball bearings operating at temperatures above 200 F. over prolonged periods of time. These and other objects achieved by this invention will become apparent in the following detailed description thereof.

We have discovered that a grease composition having improved performance life at temperatures above 200 F. can be prepared by dispersing a metal soap of an organic acid and a metal salt of a dithiophosphoric acid ester in a lubricating oil. The improved grease composition of our invention therefore comprises a dispersion of a metal soap of an organic acid and a metal salt of a dithiophosphoric acid ester in a lubricating oil. We have found that the operating life of a hearing when lubricated with a composition of our invention is markedly increased over the operating life of a bearing lubricated with competitive compositions.

The lubricating oil ingredient in the grease composition provided by this invention may be any of the hydrocarbon oils of lubricating grade, such as those customarily used in compounding greases. While the lubricating oil, in most instances, is a mineral lubricating oil, synthetic lubricants such as polymerized olefins, polyalkylene oxides such as polypropylene oxide, polymerized sulfides such as polypropylene sulfide, polymerized glycols such as polyethylene glycol, esters of di-carboxylic acids such as bis- (2-ethylhexyl)sebacate, and the like can be employed. The oil may be a refined or semi-refined parafiinic-, naphthenic-, or asphalt-base oil having a viscosity of about 50 to 4000 SUS at 100 F. If desired, a blend of oils of suitable viscosity may be employed instead of a single oil, by means of which any desired viscosity within the range of 50 to 4000 SUS at 100 F. may be secured. The viscosity of the oil has little effect on the dropping point of the compositions, but more viscous oils produce compositions having greater stickiness and adhesive properties than do the lighter oils. The oil content of the composition prepared according to this invention comprises about 50 to about 90 percent or more by weight of the total composition. The particular oil as well as the exact amount of oil employed depends upon the characteristics desired in the final composition.

The metal soaps which are employed in the composition of the invention are preferably those selected from the group consisting of sodium, lithium, barium, and strontium soaps prepared from an organic acid having between about 12 and 32 carbon atoms. The acid may he saturated or unsaturated and may contain substituents such as hydroxyl groups. The aliphatic normal fatty acids are preferred. Examples of some of the normal fatty acids are lauric, myristic, palmitic, stearic, arachidic, behenic, carnaubic, cerotic, melissic, psyllaic, and the like. We can use the soap of either a substantially pure fatty acid or mixtures of fatty acids such as those obtained from the various fatty oils and fats such as cottonseed oil, rapeseed oil, animal oils, fish oils, lard, tallow, etc. The saturated fatty acids such as those obtained from hydro genated oils of vegetable, animal and marine extraction can also be used. For example, we can use the metal soap of the fatty acids obtained by the hydrogenation of a vegetable oil, such as castor oil, or a fish oil, such as sardine oil, herring oil, cod oil, menhaden oil and the like. The hydrogenation of these oils is not a part of this invention but may be carried out by various known means such as for example, the process described on pages 372 to 430 of Hydrogenation of Organic Substances, third edition, by Carleton Ellis, D. Van Nostrand Co., Inc., New York (1930).

Since the use of a pure fatty acid is generally too expensive to employ in preparing a soap for making a grease, it is preferred to employ commercially available mixtures of predominantly saturated fatty acids such as are obtained, for example, in hydrogenated fish oil fatty acids. These acids represent distilled cuts of mixtures of fatty acids containing variable amounts of C to C acids. We have found that a grease of the invention prepared from the sodium soap of a technical grade of stearic acid (Hydrofol Acid 150, Archer-Daniels-Midland Co, Minneapolis 2, Minn.) having a maximum iodine value of 3 has an excellent performance life.

A series of other commercially available organic fatty acids derived from hydrogenated animal, vegetable and marine oils suitable for use in the preparation of soaps for use in the composition of the invention appear in the trade, among which are other Hydrofol Acids (Archer- Daniels-Midland Co., Minneapolis 2, Minn.) and Hyfac Fatty Acids (Emery Industries, Inc., Cincinnati, Ohio).

The soaps are formed by saponifying the acid or the fat with a base such as sodium, lithium, barium or strontiurn hydroxide. The amount of the soap employed is sufficient to thicken the lubricating oil to the consistency of a grease. In general, the soap content comprises about 5 to about 50 percent by weight of the total composition. Amounts between about 15 and about 35 percent are preferred. The weight ratio of soap to the metal salt of the dithiophosphoric acid ester may vary over wide limits. The preferred weight ratio of soap to metal-thiophosphate ester, however, is between about 1:1 and about 4:1.

The metal salt of the dithiophosphoric acid ester which can be used in accordance with the invention is preferably one whose salt forming metal is selected from Group II of Mendeleeffs arrangement of the elements, preferably calcium, barium or zinc. The metal salt of the dithiophosphoric acid ester can be conventionally prepared by reacting a basic divalent metal compound, usually a metal oxide, hydroxide, sulfide or carbonate, with an acidic thiophosphoric acid ester. The acidic thiophosphoric acid ester can be prepared by any known means such as by reacting phosphorus pentasulfide with an alcohol or a phenol. The organic groups of the acid esters can be alkyll, cycloalkyl, aryl, aralkyl or alkaryl radicals which contain from about 3 to 30, preferably about 6 to 14 carbon atoms, and may be further substituted in the organic portion. Suitable alcohols which can be employed in preparing the acid esters include isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, nhexyl alcohol, dimethylbutyl alcohol, n-heptyl alcohol, l-octanol, 2-octanol, Z-ethyl-L-hexanol, oxo octyl alcohols, Z-propyl-l-pentanol, n-nonyl alcohol, l-decanol, 1- dodecanol, l-hexadecanol, l-octadecanol, cyclopentanol, cyclohexanol, cycloheptanol, methyl cyclopentanol, methyl cyclohexanol, propyl cyclohexanol, 2-phenylhexanol, Z-phenyloctanol and mixtures of two or more such alcohols. Other hydroxyl-containing compounds which can be reacted with the phosphorus sulfide include phenols and alkylated phenols including phenol, mand p-cresol, 2,4- and 2,5- xylenol, 2,4-dimethyl-6-tertbutylphenol, 2,4-di-tert-butylphenol, 2,6-di-tert-butyl-4- methylphenol, dipropylphenol, dibutylphenol, dioctylphenol, tri-isobutylphenol, amylphenol, hexylphenol, tertoctylphenol, decylphenol, dodecylphenol, hexadecylphenol, octadecylphenol, and the like.

Example of esters of dithiophosphoric acids which can be reacted with the group 11 metal oxides or hydroxides are Diisopropyl dithiophosphoric acid Di-n-butyl dithiophosphoric acid Diisobutyl dithiophosphoric acid Di-n-hexyl dithiophosphoric acid Di l,3-dimethylbutyl dithiophosphoric acid Di-n-hepty dithiophosphoric acid Di-n-octyl dithiophosphoric acid Di-tert-octyl dithiophosphoric acid Di-(oxo octyl) dithiophosphoric acid Di-propylamyl dithiophosphoric acid Di-ethylhexyl dithiophosphoric acid Octyl decyl dithiophosphoric acid Didecyl dithiophosphoric acid Di-n-nonyl dithiophosphoric acid Didecyl dithiophosphoric acid Didodecyl dithiophosphoric acid Dihexadecyl dithiophosphoric acid Dioctadecyl dithiophosphoric acid Di-cyclopentyl dithiophosphoric acid Di-cyclohexyl dithiophosphoric acid Di-cycloheptyl dithiophosphoric acid Di-(methylcyclopentyl dithiophosphoric acid Di-(methylcyclohexyl) dithiophosphoric acid Di-(isopropylcyclohexyl) dithiophosphoric acid Di-(Z-phenylhexyl) dithiophosphoric acid Di-(2-phenyloctyl) dithiophosphoric acid Di-(phenyl) dithiophosphoric acid Dinaphtyl dithiophosphoric acid Di-(methylphenyl) dithiophosphoric acid Di-(2,4-dimethylphenyl) dithiophosphoric acid Di-(2,4-di-methyl-6-tert-butylphenyl) dithiophosphoric acid Di-(2,4-di-tert-butylphenyl) dithiophosphoric acid Di-(2,6-di-tert-butyl-4smethylphenyl dithiophosphoric acid Di-(isopropylphenyl) dithiophosphoric acid Di-(n-butylphenyl) dithiophosphoric acid Di-(2,4,6-tri-isobutylphenyl) dithiophosphoric acid Di-(n-amylphenyl dithiophosphoric acid Di-(n-hexylphenyl) dithiophosphoric acid Di-(tert-octylphenyl) dithiophosphoric acid Di-(n-decylphenyl) dithiophosphoric acid Di-(n-dodecylphenyl) dithiophosphoric acid Di-(n-hexadecylphenyl) dithiophosphoric acid Di-(n-octadecylphenyl) dithiophosphoric acid A grease composition having an especially long performance life at a temperature above 200 F. is obtained when the metal soap is the sodium soap of hydrogenated fish oil fatty acids and the metal salt of the dithiophosphoric acid ester is a zinc salt of a dialkyl dithiophosphoric acid wherein each of the alkyl radicals are derived from alcohols containing from 6 to 8 carbon atoms.

Thus, a preferred combination of soap and salt comprises the sodium soap of hydrogenated fish oil fatty acids and the zinc salt of a di-(C to C alkyl dithiophosphoric acid. A particularly suitable zinc dithiophosphate which may be employed to advantage with the sodium soap is the zinc salt obtained from a mixed dithiophosphate prepared by reacting a technical mixture of alcohols having an average of 6 to 8 carbon atoms with phosphorus pentasulfide.

The amount of the metal salt of the dithiophosphoric acid ester incorporated in the lubricating oil according to the invention depends to some extent upon the amount of metal soap used. In view of the fact that the amount of metal soap used in any particular instance varies to some extent depending upon the characteristics desired in the final grease composition, it is difficult to state on a weight basis an amount of metal salt of dithiophosphoric acid ester incorporated in the lubricating oil according be the optimum amount in all instances. In general, it is not necessary to use more than about 30 percent of the metal salt of the dithiophosphoric acid esters. Amounts within the range of 5 to 30 percent by weight are satisfactory, the preferred amount being about 5 to about 15 percent by Weight based on the Weight of the total composition. The preferred weight ratio of soap to the metal salt of the dithiophosphoric acid ester is between about 1:1 and about 4:1. It will be understood, of course, that when commercially available oil solutions of metal thiophosphate esters are used the optimum amount of commercial materials will be increased according to the metal salt content thereof. For example, an oil solution of a zinc dialkyldithiophosphate which contains 57 percent by weight of the metal salt can be used in amounts up to about 50 percent by weight. In order to incorporate between about 5 and about 15 percent by weight of the metal salt in a grease composition when using such a commercially available product, one would be required to use about 8.8 to about 26.4 percent by weight of the commercial product. In any event, the amount of the metal thiophosphate ester used is sufiicient to substantially increase the high temperature performance life of the grease.

While the compositions produced according to this invention are satisfactory with respect to oxygen stability in some instances, it is frequently desirable to employ a small amount of an oxidation inhibitor such as a diaryl amine. As examples of some of the diaryl amines which can be used in=the compositions of this invention may be mentioned diphenylamine, phenyl alpha naphthylamine, phenyl beta naphthylamine, alpha alpha-, alpha beta-, beta betadinaphthylamines, and the like. Other diaryl amines as well as their derivatives wherein one or more hydrogen atoms on one or both of the aromatic nuclei are replaced by a substituent group may be used. The substituting group may, for example, be one selected from the class of aryl, alkyl, amino, aryloxy and alkyloxy radicals, so long as the presence of the substituent does not render the diaryl amine insoluble in oil, or soluble in water or otherwise adversely affect the effectiveness of the diaryl amine. The amount of the diaryl amine employed will depend to a large extent upon the severity of the conditions to which the composition is subjected, as well as the particular diaryl amine used. For instance, when the composition is subjected to prolonged use under oxidizing conditions, the diaryl amine requirement will be much greater than when relatively mild non-oxidizing conditions are encountered. When a diaryl amine is desired, it is employed in an amount between about 0.1 and 1.5 percent by weight based upon the weight of the total composition. In any case, when an inhibitor is used, it is added in an amount sufficient to substantially inhibit oxidational deterioration.

Other additives may also be incorporated in the grease to improve other specific properties. Thus, rust preventives, extreme pressure agents, etc., may be added to obtain the desired properties.

From the foregoing it will be apparent that the grease constituting our invention should contain about 5 to about 50 percent and preferably about 15 to about 35 percent of the specified soap thickening agent and about 5 to about 30 percent and preferably about 5 to about 15 percent of metal dithiophosphoric acid ester. The balance of the composition is a lubricating oil together with minor amounts of conventional additives in case such other additives are desired.

In compounding the compositions of the present invention, various compounding and blending procedures may he used. A batch or continuous method of manufacture may be used. In accordance with one embodiment, mineral oil, the soap and the metal thiophosphate ester are introduced into a suitable mixing device such as a paint mill or a colloid mill. The mixture is then repeatedly passed through the mill until the desired degree of dispersion is obtained. The oxidation inhibitor, if used, is advantageously incorporated in the mineral oil subsequent to compounding with the soap and metal thiophosphate ester. According to another embodiment the soap is prepared in the presence of at least a part of the lubricating oil. According to a preferred embodimerit, the organic acids are saponified in a pressure vessel at 100 to 300 pounds per square inch in the presence of about one third of the lubricating oil at a temperature of about 320 F. Glycerin which is obtained upon saponifying a fat, particularly when an excess of saponifying base is employed is desirably retained in the grease composition in that it increases the dropping point of the final grease composition. When fatty acids are used glycerin may be added for the same purpose. The glycerin can comprise about 1 to about 3 percent by weight of the total composition. The reaction mass is then transferred to an open kettle where dehydration is eifected by heating. The remainder of the oil is added to this mass while heating at a temperature between 300 and 420 F. The mixture is then cooled to about 200 F. The metal salt of the dithiophosphoric acid ester is then thoroughly admixed with the oil-soap reaction mass. Biphenylamine, or other oxidation inhibitor, is then added after which the grease composition is milled in a paint mill or colloid mill until the desired degree of dispersion is obtained.

The increased performance life at an elevated temperature of grease compositions of the present invention as compared with a similar composition containing no metal dithiophosphate ester will be demonstrated hereinbelow in an anti-friction bearing test machine. This machine consists essentially of two flat-rimmed steel wheels, each containing two No. 6210 ball bearings, mounted on two parallel spindles, one above the other, and loaded through a system of levers and fulcrum plates by tangential contact of the wheels. The lower spindle with its wheel is connected to the loading system, and the upper assembly is brought to bear upon the lower by turning down two large screws until it counterbalances the chosen loading weight, which in these tests was 1000 pounds. To insure a fixed temperature of 250 F, the wheels are enclosed in an insulated box and heated by thermostatically controlled ring heaters surrounding the hubs. A cartridge heater in the rear of each spindle compensates for the heat loss through the heavy steel structure. Thermocouples are situated in grooves in the spindles and contact each hearing. A pulley on the upper wheel and two appropriate holes in the side of the insulated box provide for a belt driven by means of a motor mounted on the outside. A single charge of grease grams) is packed into each ball bearing. The test runs continue as long as the bearings remain lubricated by the original charge, but with several interruptions for inspections, to observe developments and changing conditions. Finally,

the runs are terminated and grease failure is declared when the race paths are found to be dry, a condition sometimes signalized by a sudden temperature rise in the hearing.

In preparing the composition to illustrate the invention the mineral oil component comprised a lubricating oil having as typical properties an API gravity of 29.8, a viscosity of 305 SUS at F. and 54.5 at 210 F., a flash point of 455 F., a fire point of 515 F., and a pour point of +5 F. The grease compositions were prepared according to the procedure set forth as the preferred embodiment described above. According to this embodiment a technical grade of stearic acid (Hydrofol Acid was saponified with sodium hydroxide in a pressure vessel at 100 to 300 pounds per square inch in the presence of about one third of the lubricating oil and glycerin at a temperature of about 320 F. The saponified mass was then dehydrated by further heating at 300 to 420 F. in an open kettle. After adding the remainder of the oil, the mixture was cooled to about 200 F. The zinc dithiophosphoric acid ester and diphenylamine were then thoroughly blended with the oil-soap reaction mass. Milling was continued until a homogeneous grease was obtained. In preparing the comparative composition containing no zinc salt, the procedure, was identical to that just given except that no zinc salt was employed. The approximate make-up and performance lives of grease compositions made in accordance with the above procedure are set forth in Table I.

Table I Composition, percent by weight A B C Lubricating oil 70. 07 61.00 61. 00 Sodium soap of stearic acid (Hydroi'ol Acid 150) 27. 12 23. 62 23.62 Glycerin 1. 78 1. 55 1. 55 Zinc salt of di-(1,3-dimetl1ylbutyl) dithiophosphoric acid 12. 93 Zinc salt of di (CB to C3 mixed alkyl) dithiophosphoric acid (57% zinc salt- 43% solvent oil) 12. 93 Diphenylamine- 0. 90 0. 90 Ratio of sodium soap to zinc salt 1. 82: 1 1. 82:1

*(3.2;1 Performance test Hours to Failure 4, 017 11, 679 8,143

*Based on 57% active material.

It will be noted that compositions of the invention (Composition B and Composition .C) had performance lives of 11679 and 8143 hours, respectively, and that Composition A, which contained no zinc dithiophosphate had a performance life of only 4017 hours. The compositions of the invention thus had performance lives of two to three times the life of the comparative composition.

Typical inspection characteristics of Compositions A, B and C are set forth in Table II.

Other grease composition within the vention are illustrated in Table III.

scope of the in- Table III Composition, percent by weight Lubricating oil.

Metal soap:

Sodium laur e Lithium myr fate Zinc di-(2-pheny1hexyl) dithiophosphate Zinc di-(tert-octylphenyl) dithiophosphate Zinc dinaphthyl dithiophosphate Ratio of metal soap to metal organo dithiophosphate While our invention has been described with reference to various specific examples and embodiments, it will be understood that the invention is not limited to such exam pies and embodiments and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A grease composition having an improved performance life at a temperature above about 200 F. comprising a dispersion in about 50 to about 80 percent by weight of a lubricating oil base of about 15 to about 35 percent by weight of a sodium soap of a C fatty acid and about 5 to about percent by weight of a zinc salt of a di-(C to C alkyl) dithiophosphoric acid, the weight ratio of the sodium soap to the zinc salt being between about 1:1 and about 4:1.

2. A grease composition having an improved performance life at a temperature above about 200 F. comprising about 50 to about 80 percent by weight of a lubricating oil base of about 15 to about percent by Weight of a sodium soap of a C fatty acid, about 5 to about 15 percent by weight of a zinc salt of a di-(C to C mixed alkyl) dithiophosphoric acid, about 1 to about 3 percent by weight of glycerin and about 0.1 to about 1.5 percent by weight of diphenylamine, the weight ratio of the sodium soap to the zinc salt being between about 1:1 and about 4:1.

3. A grease composition having an improved performance life at a temperature above about 200 F. comprising a dispersion in about to about percent by weight of a lubricating oil base of about 15 to about 35 percent by weight of a sodium soap of a C fatty acid, about 5 to about 15 percent by weight of a zinc salt of di-(1,3-dimethylbutyl) dithiophosphoric acid, about 1 to about 3 percent by weight of glycerin and about 0.1 to about 1.5 percent by weight of diphenylamine, the weight ratio of the sodium soap to the zinc salt being between about 1:1 and about 4:1.

References Cited by the Examiner UNITED STATES PATENTS 2,364,283 12/44 Freuler 25232.7 2,899,388 8/59 Nelson et a1 25232.7

OTHER REFERENCES Manufacture and Application of Lubricating Greases, by Boner, Reinhold Pub. Corp., New York, 1954, page 43.

DANIEL E. WYMAN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,203,897 August 31, 1965 Henry A Ambrose et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 18, for "incorporated in the lubricating oil according" read based upon the weight of the oil, which will column 7, lines 33 and 34, for "comprising about" read comprising a dispersion in about e Signed and sealed this 14th day of June 1966 (SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Attesting Officer 

1. A GREASE COMPOSITION HAVING AN IMPROVED PERFORMANCE LIFE AT A TEMPERATURE ABOVE ABOUT 200%F. COMPRISING A DISPERSION IN ABOUT 50 TO ABOUT 80 PERCENT BY WEIGHT OF A LUBRICATING OIL BASE OF ABOUT 15 TO ABOUT 35 PERCENT BY WEIGHT OF A SODIUM SOAP OF A C18 FATTY ACID AND ABOUT 5 TO ABOUT 15 PERCENT BY WEIGHT OF A ZINC SALT OF A DI-(C6 TO C8 ALKYL) DITHIOPHOSPHORIC ACID, THE WEIGHT RATIO OF THE SODIUM SOAP TO THE ZINC SALT BEING BETWEEN ABOUT 1:1 AND ABOUT 4:1. 